Current processes for the amination of alcohols and diols typically use heterogeneous catalysts comprising supported transition metals with known hydrogenation/dehydrogenation activity and/or acidic compositions, in particular, zeolites, mixed oxides and metal phosphates. Unfortunately, such catalyst systems present numerous process limitations. For example, catalysts containing transition metals typically yield by-product amines and olefins which may cause catalyst deactivation and often produce undesireable aldehyde-type by-products. Acidic catalysts are usually non-selective in alcohol amination reactions yielding the corresponding ether, unsaturated hydrocarbon, polymeric products and scrambled amines as by-products formed via transalkylation and disproportionation reactions.
Acidic catalysts also tend to dehydrate alcohols to form olefin or ether by-products thereby reducing the yield of the desired N-alkylation product. Alkene formation can be reduced somewhat by operating the process at lower temperatures. Unfortunately, lower reaction temperatures necessitate use of a lower ratio of amine/alcohol in order to achieve sufficiently high amine conversion Additionally, both acidic and dehydrogenation type catalysts inherently require some recycle of unconverted reactants.
Several processes have been developed using acidic metal phosphate catalysts. More particularly. phosphates of boron, aluminum and trivalent iron have been proposed for use in intramolecular cyclic dehydration reactions and other condensation reactions involving amine compounds. Examples of such reactions are found in U.S. Pat. No. 4,117,227 which discloses conversion of an N-substituted diethanolamine to the corresponding N-substituted morpholine. Additionally, U.S. Pat. No. 4,049,657 discloses the reaction of piperidine with ethanolamine over metal phosphate catalysts to produce N-aminoethyl piperidine.
U.S. Pat. No. 4,082,805, relates to a process for the production of aliphatic amines wherein a C.sub.1 to C.sub.5 alcohol or ether is reacted with ammonia in the presence of a crystalline aluminosilicate catalyst having the structure of ZSM-5, ZSM-11 or ZSM-21. Preferred catalysts have a high silica to alumina ratio typically greater than 5 and preferably greater than 30. The reaction is effected at a temperature between 300.degree. C. and about 500.degree. C. and a pressure between atmospheric and 1000 psig. The relative feed rates, expressed in grams per hour of alcohol or ether to ammonia, typically range from 1:1 to about 5:1.
U.S. Pat. No. 4,501,889, assigned to Air Products and Chemicals, Inc., discloses a process for preparing morpholine compounds by reacting 2-(2-aminoethoxy)ethanol in the presence of an effective amount of catalyst selected from the group consisting of the pyrophosphate, monohydrogen phosphate and the dihydrogen phosphate of strontium, copper, magnesium, calcium, barium, zinc, aluminum, lanthanum, cobalt, nickel, cerium and neodymium and mixtures thereof. Preferred catalysts are the soluble metal salts of strong acids such as metal nitrates in substantially stoichiometric proportion to the phosphate.